Large‐Eddy Simulation of the Spray‐Laden Hurricane Boundary Layer: II. Spray Impacts on Air‐Sea Fluxes

Abstract

The effects of spray on air‐sea fluxes in high‐wind environments have been studied for decades, and several models have been developed and implemented. Owing to the difficulties in making direct measurements in these conditions, however, many process‐level details of spray‐turbulence interaction remain unknown, and certain assumptions must often be made regarding droplet lifetimes and their interaction with background conditions. This work represents Part II of a study where the spray‐laden hurricane boundary layer is resolved using large‐eddy simulation. Here we focus on the effects of spray on air‐sea fluxes of heat, moisture, and momentum, and investigate the potential modifications to the bulk flux coefficients CD ${C}_{D}$ , CH ${C}_{H}$ , and CE ${C}_{E}$ . The simulations show an increase in the drag coefficient CD ${C}_{D}$ —a numerical artifact reflecting the fact that the winds must accelerate all newly formed droplets. Unresolved wave breaking and near‐surface turbulence are likely important factors not contained in the simulations. Spray impacts on thermodynamic fluxes, on the other hand, are largely controlled by background humidity and suspended spray mass, and we demonstrate a process where spray can actually limit its own influence by saturating the boundary layer. The simulations are also used to show that bulk models which rely on assuming that all spray‐mediated fluxes are caused by re‐entrant droplets might be inaccurate, since they do not account for the vertically distributed source/sink of heat and moisture caused by the potentially large number of small droplets which have escaped the surface layer.